Current early-age concrete evaluation devices, such as the maturity meter, cannot be applied for the detection and evaluation of cracks and damage for the maintenance period. Some other early-age concrete evaluation devices, such as ultrasonic wave velocity meters, require bulky equipment and are not suitable for the health monitoring of in-situ, large-scale concrete structures.
The current maturity meter measures the hydration heat of a concrete structure and the hydration time at early-age to estimate the strength development of a concrete structure. An ultrasonic velocity meter evaluates some physical properties of a concrete structure by measuring the velocity of ultrasonic waves propagated inside the concrete structure.
Compressive test equipment determines the compressive strength data of concrete by directly compressing and crushing the concrete specimens (structure) but, due to the press method, equipment and other uncertain factors, large amounts of concrete specimens are needed for the test which is time-consuming and effort consuming.
The present technological methods to evaluate the strength of concrete at early-age can be classified into two categories: (1) destructive method that crushes the concrete for strength testing and (2) non-destructive testing.
Two popular non-destructive methods to evaluate the early-age strength development of concrete are the hydration heat-based method and the ultrasonic wave velocity-based method. Hydration heat-based method evaluates the early-age strength development of concrete by measuring the hydration heat and recording the hydration time. This kind of method cannot be applied to the health monitoring of concrete structure after the concrete strength is fully developed.
The ultrasonic velocity-based method applies an ultrasonic meter on the surface of concrete structure to measure the velocity of the ultrasonic waves from the surface to evaluate the concrete strength. The shortcoming of this method is that the variation of the wave velocity of the ultrasonic waves is not sensitive to the strength of the concrete. A ten percent increment of strength may only result in less than one percent increment of the wave velocity.
Early-age concrete performance is an important and critical issue for the construction of the concrete structures. The construction speed and the quality evaluation of concrete at an early-age are the major concerns for the construction of civil concrete structures. After the concrete is cured, the detection of the existence and growth of cracks and damage is another important issue for the maintenance of civil concrete structures.
It is an object of the present invention, therefore, to extend the lifetime of concrete structures. It is a further object of the invention to enhance the safety of concrete buildings. It is also an object of the present invention to reduce the maintenance effort and cost for concrete structures.